This invention relates to wind turbines, which are commonly used as a means to generate electric power, particularly in areas remote from any other viable electric power generation source.
A number of wind turbine systems are known, some of which are in use. These fall into two broad types, depending primarily on the orientation of the turbine axis of rotation: the axis is either horizontal, or it is vertical. In both structures, the rotation of the wind turbine is transmitted to an electrical generating system to produce power. This invention is concerned with a wind turbine structure in which the wind turbine axis of rotation is essentially vertical.
In horizontal axis wind turbines, a rotatable blade system, which in appearance is often much like an aircraft propeller, is caused to rotate about horizontal axis, which is generally carried at the top of a suitable tower structure. The axis of rotation consequently is more or less in line with the wind direction. Exemplary arrangements of this type are described in EP 0 015 131 and in WO 97/39240. It has also been proposed to modify the horizontal wind turbine by changing the turbine axis to vertical, and providing a structure which will cause a flow of air over the wind turbine. The structure can be arranged to provide an air flow which can be either upward or downward in direction. Exemplary arrangements of this type are described in U.S. Pat. No. 4,017,205, U.S. Pat. No. 4,018,535, U.S. Pat. No. 4,036,916 and FR 2 588 317 (all upward air flow) and in U.S. Pat. No. 4,116,581 (downward air flow).
In true vertical axis wind turbines, a blade system is carried on a vertical axis of rotation which is substantially perpendicular to the wind direction. Several arrangements of this type are known, in which blade surfaces are attached to a suitable shaft, and static surfaces are used to direct the wind flow past the blade surfaces. Exemplary arrangements of this type are shown in U.S. Pat. No. 4,088,419, U.S. Pat. No. 4,156,580, U.S. Pat. No. 4,365,929 and JP 08 232 831. An alternative vertical axis wind turbine in which the blades are bow-shaped and attached only at their ends to a rotatable shaft is also known. Exemplary arrangements of this type, known as the Darrius type, are described in U.S. Pat. No. 1,835,018 and CA 1,151,072.
These known wind turbines suffer from a number of disadvantages. First, since the wind rarely always blows in the same direction, for most of these devices it is also necessary to provide a means to align the wind turbine with the wind: for example in EP 0 015 131 the whole structure can be rotated. The Darrius type does not have this limitation. Second, most of these devices, including the Darrius type, are not efficient in converting wind energy into available rotary energy to drive a generator. Third, at least in part due to their inefficiency, these turbines require a significant airflow in order to generate power, and do not operate under low wind speed conditions. As a further complication, even when there is sufficient wind velocity available, the Darrius type has to be started into rotation by a powering device, since it is not self starting. Fourth, all of these devices have a range of safe wind speeds: if the wind speed becomes too high the turbines simply run faster until damage occurs to the device unless steps are taken to both shut them down and lock the turbine to prevent it rotating. Additionally, apart from means to channel the wind flow through the turbine, no attention appears to have been paid at all to the air flow patterns around the turbines, and in particular to the air flow pattern down wind from the turbine.
This invention seeks to overcome at least some of these disadvantages by providing a vertical axis wind turbine structure which uses the available wind air flow more efficiently, which will respond to wind speeds below the operational limit for most known wind turbines, and which will disengage power transfer due to loss of the vortex if the wind speed becomes too high for safe operation. This invention seeks to control the air flow pattern down wind of a vertical turbine, in particular to provide a structure including a wind turbine which creates a vortex condition down wind of the turbine which enhances the air flow past the vertical turbine. In the vertical axis wind turbine structure of this invention, a rectangular shaped turbine with four orbiting panels is mounted to rotate at the top of a pyramidal base structure which generates a substantially horizontal vortex immediately down wind of the turbine, thus enhancing the air flow past the turbine. Hence by defeating an air flow pattern that is akin to an aerodynamic lift condition, a low pressure zone moving upwardly over the down wind face of the pyramidal base structure is combined with a high pressure zone near the apex of the pyramid to create the down wind vortex.
Thus in its broadest embodiment this invention seeks to provide a vertical axis wind turbine structure comprising in combination:
(a) a substantially square pyramidal base structure, having an apex and a base surface defining a substantially horizontal plane;
(b) a substantially triangular face joined to each of the four edges of the base surface and to the adjacent triangular faces;
(c) a turbine structure constructed and arranged to rotate about a vertical axis; and
(d) means to utilise the rotation of the turbine to provide useful work; wherein:
(i) the four edges of the base surface are the same length;
(ii) the four triangular faces are inclined at the same included angle to the base surface;
(iii) the included angle between each of the four triangular faces and the base surface is from 45xc2x0 to 55xc2x0;
(iv) the turbine structure extends upwardly from the apex of the pyramid;
(v) the turbine contains four elongate wind panels formed in two parts, each of which is attached along a first elongate edge to the turbine axis and along a second elongate edge to the second part; and
(vi) the two parts of each elongate wind panel are joined into an L-shaped cross-section, in which the two arms are of substantially the same width.
Preferably, the included angle between each of the four triangular faces and the base surface is about 50xc2x0. More preferably, the included angle between each of the four triangular faces and the base surface is from 49xc2x030xe2x80x2 to 52xc2x030xe2x80x2.
Preferably, the four triangular faces are flat. More preferably, each of the four triangular faces is creased inwardly on a line from the pyramid apex to the midpoint of the base surface edge, and the crease angle is from about 1xc2x0 to about 2xc2x0. Most preferably, each of the four triangular faces is creased inwardly on a line from the pyramid apex to the midpoint of the base surface edge, and the crease angle is about 1xc2x030xe2x80x2.